Power amplifier circuit

ABSTRACT

A power amplifier circuit includes a first power supply terminal electrically connected to a first power amplifier; a second power supply terminal electrically connected to a second power amplifier subsequent to the first power amplifier; a first external power supply line configured to electrically connect a power supply circuit configured to output a power supply potential corresponding to an amplitude level of a high-frequency input signal and the first power supply terminal; and a second external power supply line configured to electrically connect the power supply circuit and the second power supply terminal. An inductance value of the first external power supply line is higher than an inductance value of the second external power supply line.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2019-200941 filed on Nov. 5, 2019. The content of this application is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to a power amplifier circuit. In a power amplifier circuit installed in a wireless communication terminal device, reductions in power consumption are necessary. As one method of reducing power consumption, there is an envelope tracking method in which a power supply potential of the power amplifier circuit is controlled in accordance with an amplitude level of a high-frequency signal.

Japanese Unexamined Patent Application Publication No. 2018-37839 discloses a technique in which, in each of power amplifiers connected in multiple stages, a difference between the phase of a high-frequency signal and the phase of a power supply potential is reduced. Specifically, Japanese Unexamined Patent Application Publication No. 2018-37839 discloses a technique in which, of the power amplifiers connected in multiple stages, the phase of a power supply potential of a subsequent-stage power amplifier is delayed.

The fourth generation mobile communication systems (4G, such as long term evolution (LTE) and LTE-Advanced) are currently being implemented. Furthermore, the fifth generation mobile communication system (5G) is being put to practical use.

In the 4G, a frequency band of an envelope tracking modulated signal (power supply potential) ranges from 10 MHz to 20 MHz and ranges from 30 MHz to 40 MHz at the maximum. On the other hand, in the 5G, a frequency band of a power supply potential is asked to be up to 100 MHz or more as described in Ji-Seon Paek, and other 13 authors, “15.1 An 88%-Efficiency Supply Modulator Achieving 1.08 μs/V Fast Transition and 100 MHz Envelope-Tracking Bandwidth for 5G New Radio RF Power Amplifier”, 2019 IEEE International Solid-State Circuits Conference, DIGEST OF TECHNICAL PAPERS, Feb. 19, 2019, pp. 238-239.

Thus, since the frequency band of the power supply potential in the 5G is wider than that in the 4G, it is conceivable that the technique disclosed in Japanese Unexamined Patent Application Publication No. 2018-37839 has difficulty in dealing with the frequency band of the power supply in the 5G. Specifically, in a previous-stage power amplifier of the power amplifiers connected in multiple stages, the phase of a power supply potential may get ahead of the phase of a high-frequency signal. As a result, there is a possibility that distortion may occur in the high-frequency signal.

BRIEF SUMMARY

In view of the above, the present disclosure has been made and reduces a possibility that distortion may occur in a high-frequency signal.

A power amplifier circuit according to one aspect of the present disclosure includes a plurality of power amplifiers connected in multiple stages and configured to amplify a high-frequency input signal and output an amplified high-frequency output signal; a first power supply terminal electrically connected to a first power amplifier of the plurality of power amplifiers; a second power supply terminal electrically connected to a second power amplifier subsequent to the first power amplifier of the plurality of power amplifiers; a first external power supply line configured to electrically connect a power supply circuit configured to output a power supply potential corresponding to an amplitude level of the high-frequency input signal and the first power supply terminal; and a second external power supply line configured to electrically connect the power supply circuit and the second power supply terminal. An inductance value of the first external power supply line is higher than an inductance value of the second external power supply line.

A power amplifier circuit according to one aspect of the present disclosure includes a plurality of power amplifiers connected in multiple stages and configured to amplify a high-frequency input signal and output an amplified high-frequency output signal; a power supply terminal configured to receive a power supply potential corresponding to an amplitude level of the high-frequency input signal; a first internal power supply line configured to electrically connect a first power amplifier of the plurality of power amplifiers and the power supply terminal; and a second internal power supply line configured to electrically connect a second power amplifier subsequent to the first power amplifier of the plurality of power amplifiers and the power supply terminal. An inductance value of the first internal power supply line is higher than an inductance value of the second internal power supply line.

A power amplifier circuit according to one aspect of the present disclosure includes a plurality of power amplifiers connected in multiple stages and configured to amplify a high-frequency input signal and output an amplified high-frequency output signal; a second power supply terminal configured to receive a power supply potential corresponding to an amplitude level of the high-frequency input signal; a second internal power supply line having one end electrically connected to the second power supply terminal and another end electrically connected to a second power amplifier of the plurality of power amplifiers; and a first internal power supply line having one end electrically connected to the other end of the second internal power supply line and another end electrically connected to a first power amplifier previous to the second power amplifier of the plurality of power amplifiers.

The present disclosure enables a reduction in the possibility that distortion may occur in a high-frequency signal.

Other features, elements, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of embodiments of the present disclosure with reference to the attached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a configuration of a transmission circuit including a power amplifier circuit according to a comparative example;

FIG. 2 illustrates a circuit configuration of the power amplifier circuit according to the comparative example;

FIG. 3 illustrates a circuit configuration of a power amplifier in the power amplifier circuit according to the comparative example;

FIG. 4 illustrates the power amplifier circuit according to the comparative example;

FIG. 5 illustrates an equivalent circuit of the power amplifier circuit according to the comparative example;

FIG. 6 illustrates circuit simulation results of the equivalent circuit of the power amplifier circuit according to the comparative example;

FIG. 7 illustrates circuit simulation results of the equivalent circuit of the power amplifier circuit according to the comparative example;

FIG. 8 illustrates a circuit configuration of a power amplifier circuit according to a first embodiment;

FIG. 9 illustrates the power amplifier circuit according to the first embodiment;

FIG. 10 illustrates circuit simulation results of an equivalent circuit of the power amplifier circuit according to the first embodiment;

FIG. 11 illustrates circuit simulation results of the equivalent circuit of the power amplifier circuit according to the first embodiment;

FIG. 12 illustrates a circuit configuration of a power amplifier circuit according to a second embodiment;

FIG. 13 illustrates an example of a first internal power supply line of the power amplifier circuit according to the second embodiment;

FIG. 14 illustrates an inductor inserted in the first internal power supply line of the power amplifier circuit according to the second embodiment;

FIG. 15 illustrates a circuit configuration of a power amplifier circuit according to a third embodiment; and

FIG. 16 illustrates an equivalent circuit of the power amplifier circuit according to the third embodiment.

DETAILED DESCRIPTION

Embodiments of a power amplifier circuit according to the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not to be limited by these embodiments. Each embodiment is merely illustrative, and it goes without saying that configurations described in different embodiments can be partially replaced or combined. In second and subsequent embodiments, a description of things in common with a first embodiment is omitted, and only respects in which the second and subsequent embodiments differ from the first embodiment will be described. In particular, similar function effects achieved by similar configurations are not repeatedly described in each embodiment.

First Embodiment

Although a first embodiment will be described below, a comparative example will be described first to facilitate understanding of the first embodiment.

Comparative Example

FIG. 1 illustrates a configuration of a transmission circuit including a power amplifier circuit according to a comparative example. A transmission circuit 100 is used, for example, in a wireless communication terminal device, such as a mobile phone device, to transmit various signals, such as voice and data, to a base station. Incidentally, although the wireless communication terminal device includes a reception unit as well that receives a signal from the base station, a description of the reception unit is omitted herein.

As illustrated in FIG. 1 , the transmission circuit 100 includes a baseband circuit 101, a radio frequency (RF) circuit 102, a power supply circuit 103, a power amplifier circuit 104, a front-end circuit 105, and an antenna 106.

The baseband circuit 101 modulates an input signal S_(IN), such as voice or data, in accordance with a modulation scheme for high speed uplink packet access (HSUPA), LTE, or the like and outputs a modulated signal S_(IQ). The modulated signal S_(IQ) is an IQ signal (an in-phase (I) signal and a quadrature (Q) signal) whose amplitude and phase are represented in an IQ plane.

The RF circuit 102 outputs a high-frequency input signal RF_(IN) in accordance with the modulated signal S_(IQ) output from the baseband circuit 101. Furthermore, the RF circuit 102 detects an amplitude level of the modulated signal S_(IQ) in accordance with the modulated signal S_(IQ). Then, the RF circuit 102 outputs, to the power supply circuit 103, a control signal S_(CTRL) that controls the power supply circuit 103 so that a power supply potential V_(CC) to be supplied to the power amplifier circuit 104 reaches a level corresponding to an amplitude level of the high-frequency input signal RF_(IN). Specifically, the RF circuit 102 outputs, to the power supply circuit 103, the control signal S_(CTRL) that controls the power supply circuit 103 so that the power supply potential V_(CC) reaches a level corresponding to an envelope of the high-frequency input signal RF_(IN). In other words, the RF circuit 102 outputs the control signal S_(CTRL) for performing envelope tracking to the power supply circuit 103.

Incidentally, in the RF circuit 102, direct conversion from the modulated signal S_(IQ) to the high-frequency input signal RF_(IN) is not performed, the modulated signal S_(IQ) is converted to an intermediate frequency (IF) signal, and the high-frequency input signal RF_(IN) may be generated from the IF signal.

The power supply circuit 103 is an envelope tracking power supply circuit that generates a power supply potential V_(CC) having a level corresponding to the control signal S_(CTRL) output from the RF circuit 102, that is, a power supply potential V_(CC) having a level corresponding to the envelope of the high-frequency input signal RF_(IN) and outputs the power supply potential V_(CC) to the power amplifier circuit 104. The power supply circuit 103 can be constituted, for example, by a direct current to direct current (DC-DC) converter that generates a power supply potential V_(CC) having a level corresponding to the control signal S_(CTRL) from an input voltage.

The power amplifier circuit 104 amplifies the power of the high-frequency input signal RF_(IN) output from the RF circuit 102 to a level suitable to transmit the high-frequency input signal RF_(IN) to the base station. Subsequently, the power amplifier circuit 104 outputs an amplified high-frequency output signal RF_(OUT) to the front-end circuit 105.

The front-end circuit 105 performs filtering on the high-frequency output signal RF_(OUT), switching between the high-frequency output signal RF_(OUT) and a reception signal received from the base station, and so forth. The high-frequency output signal RF_(OUT) output from the front-end circuit 105 is transmitted to the base station through the antenna 106.

FIG. 2 illustrates a circuit configuration of the power amplifier circuit according to the comparative example. The power amplifier circuit 104 includes a first-stage first power amplifier 11 and a final-stage second power amplifier 12. Although the power amplifier circuit 104 may be implemented by a hybrid integrated circuit (which may be referred to as a module) in which a plurality of components (semiconductor integrated circuits and so forth) are mounted on one substrate, the present disclosure is not limited to this.

Furthermore, although the power amplifier circuit 104 includes two stages of power amplifiers that are the first power amplifier 11 and the second power amplifier 12, the present disclosure is not limited to this. The power amplifier circuit 104 may include three or more stages of power amplifiers. For example, the power amplifier circuit 104 may further include one or more power amplifiers inserted between the first power amplifier 11 and the second power amplifier 12.

The first power amplifier 11 may be referred to as a first stage or drive stage. The second power amplifier 12 may be referred to as a final stage or power stage.

FIG. 3 illustrates a circuit configuration of a power amplifier in the power amplifier circuit according to the comparative example. The first power amplifier 11 includes a transistor 111, a capacitor 112, and an inductor 113.

In the present disclosure, although a transistor is a bipolar transistor, the present disclosure is not limited to this. Although, as an example of the bipolar transistor, a heterojunction bipolar transistor (HBT) is given, the present disclosure is not limited to this. The transistor may be, for example, a field-effect transistor (FET). The transistor may be a multi-finger transistor including a plurality of unit transistors (also referred to as fingers) electrically connected in parallel. A unit transistor refers to a minimum component constituting the transistor.

An emitter of the transistor 111 is electrically connected to a reference potential. Although, as an example of the reference potential, a ground potential is given, the present disclosure is not limited to this.

A collector of the transistor 111 is electrically connected to one end of the inductor 113. The power supply potential V_(CC) is input to the other end of the inductor 113. The inductor 113 supplies the power of the power supply potential V_(CC) to the collector of the transistor 111. A collector current flows from the power supply potential V_(CC) to the collector of the transistor 111 through the inductor 113.

Assume that the inductor 113 has a sufficiently high impedance for a frequency band of the high-frequency input signal RF_(IN). That is, in considering the frequency band of the high-frequency input signal RF_(IN), the impedance of the inductor 113 is negligible. Furthermore, the inductor 113 keeps the high-frequency input signal RF_(IN) from coupling to the power supply circuit 103. In other words, the inductor 113 serves as a choke inductor.

The high-frequency input signal RF_(IN) is input to a base of the transistor 111 through the capacitor 112. Furthermore, a bias current I_(BIAS) is input to the base of the transistor 111.

In the transistor 111, an electrical bias state is set by the bias current I_(BIAS). The transistor 111 outputs, from the collector to the second power amplifier 12, a high-frequency signal RF_(M) obtained by performing power amplification on the high-frequency input signal RF_(IN).

A circuit configuration of the second power amplifier 12 is similar to that of the first power amplifier 11, and illustration and description thereof are thus omitted.

Referring back to FIG. 2 , the high-frequency input signal RF_(IN) is input to the first power amplifier 11 through a high-frequency signal input terminal 21. One end of a first internal power supply line 13 is electrically connected to a first power supply terminal 23. The other end of the first internal power supply line 13 is electrically connected to the first power amplifier 11 (the other end of the inductor 113 (see FIG. 3 )). The power supply potential V_(CC) is input to the first power amplifier 11 through the first power supply terminal 23 and the first internal power supply line 13. One end of a capacitor 15 is electrically connected to the first power amplifier 11 (the other end of the inductor 113). The other end of the capacitor 15 is electrically connected to the reference potential. The first power amplifier 11 outputs the amplified high-frequency signal RF_(M) to the second power amplifier 12.

The high-frequency signal RF_(M) is input from the first power amplifier 11 to the second power amplifier 12. One end of a second internal power supply line 14 is electrically connected to a second power supply terminal 24. The other end of the second internal power supply line 14 is electrically connected to the second power amplifier 12. The power supply potential V_(CC) is input to the second power amplifier 12 through the second power supply terminal 24 and the second internal power supply line 14. One end of a capacitor 16 is electrically connected to the second power amplifier 12. The other end of the capacitor 16 is electrically connected to the reference potential. The second power amplifier 12 outputs the amplified high-frequency output signal RF_(OUT) to the front-end circuit 105 through a high-frequency signal output terminal 22.

The power supply circuit 103 is electrically connected to the first power supply terminal 23 and the second power supply terminal 24 using an external power supply line 121. One end of the external power supply line 121 is electrically connected to the power supply circuit 103. On another end side of the external power supply line 121, a division has been made into a first external power supply line 121 b and a second external power supply line 121 c at a branch portion 121 a. A tip portion of the first external power supply line 121 b is electrically connected to the first power supply terminal 23. A tip portion of the second external power supply line 121 c is electrically connected to the second power supply terminal 24.

In the present disclosure, although the first external power supply line 121 b and the second external power supply line 121 c are integrally formed, the present disclosure is not limited to this. The first external power supply line 121 b and the second external power supply line 121 c may be separately formed and connected together. Furthermore, the first external power supply line 121 b and the second external power supply line 121 c do not have to be connected together. In other words, each of the other end portion of the first external power supply line 121 b and the other end portion of the second external power supply line 121 c may be directly connected to the power supply circuit 103.

FIG. 4 illustrates the power amplifier circuit according to the comparative example. Specifically, FIG. 4 illustrates the power amplifier circuit 104 that is a semiconductor integrated circuit (IC) mounted on a substrate 131 as viewed from above.

On the substrate 131, the external power supply line 121 is formed. The external power supply line 121 is divided into the first external power supply line 121 b and the second external power supply line 121 c at the branch portion 121 a.

On a lower surface of the power amplifier circuit 104 (a surface opposite to the substrate 131), the first power supply terminal 23 and the second power supply terminal 24 are provided. The first power supply terminal 23 is electrically connected to the first external power supply line 121 b. The second power supply terminal 24 is electrically connected to the second external power supply line 121 c.

The width of the first external power supply line 121 b and the width of the second external power supply line 121 c are substantially the same. Furthermore, the length of the first external power supply line 121 b and the length of the second external power supply line 121 c are substantially the same. Hence, an inductance value of the first external power supply line 121 b and an inductance value of the second external power supply line 121 c are substantially the same.

In FIG. 4 , although the first power supply terminal 23 and the second power supply terminal 24 are provided at a corner portion of the power amplifier circuit 104 that is the semiconductor integrated circuit, the present disclosure is not limited to this. The first power supply terminal 23 and the second power supply terminal 24 may be provided at a place (for example, a middle portion of a side) other than the corner portion of the power amplifier circuit 104. Furthermore, although the first power supply terminal 23 and the second power supply terminal 24 are arranged next to each other, the present disclosure is not limited to this. Another terminal (for example, a ground terminal) may be provided between the first power supply terminal 23 and the second power supply terminal 24.

FIG. 5 illustrates an equivalent circuit of the power amplifier circuit according to the comparative example. An equivalent circuit of the power amplifier circuit 104 includes inductors L₁ and L₂, resistors R₁ and R₂, and capacitors C₁ and C₂.

The inductor L₁ corresponds to an inductance component of the first external power supply line 121 b. The resistor R₁ corresponds to a resistance component (corresponding to a collector-emitter resistance component during operation, which is a value obtained by dividing a voltage supplied to the collector by a current consumed by the collector) of the transistor 111 (see FIG. 3 ) as seen from a power supply circuit 103 side. The capacitor C₁ corresponds to the capacitor 15.

The inductor L₂ corresponds to an inductance component of the second external power supply line 121 c. The resistor R₂ corresponds to a resistance component (corresponding to a collector-emitter resistance component during operation, which is a value obtained by dividing a voltage supplied to a collector by a current consumed by the collector) of a transistor in the second power amplifier 12 as seen from the power supply circuit 103 side. The capacitor C₂ corresponds to the capacitor 16.

As described above with reference to FIG. 4 , the inductance value of the first external power supply line 121 b and the inductance value of the second external power supply line 121 c are substantially the same. That is, an inductance value of the inductor L₁ and an inductance value of the inductor L₂ are substantially the same. Although it is exemplified that each of the inductance value of the inductor L₁ and the inductance value of the inductor L₂ is about 2 nH (nanohenrys), the present disclosure is not limited to this.

In general, in power amplifiers connected in multiple stages, the size of a subsequent-stage power amplifier is larger than that of a previous-stage power amplifier. In other words, the number of fingers of the subsequent-stage second power amplifier 12 is larger than that of the previous-stage first power amplifier 11. Hence, a resistance value of the resistor R₁ is higher than a resistance value of the resistor R₂. Although it is exemplified that the resistance value of the resistor R₁ is about 20Ω (ohms), the present disclosure is not limited to this. Although it is exemplified that the resistance value of the resistor R₂ is about 4Ω, the present disclosure is not limited to this. Here, the resistance value of the resistor R₁ is about five times the resistance value of the resistor R₂.

An impedance value of the capacitor C₁ is set to a value corresponding to the resistance value of the resistor R₁. Similarly, an impedance value of the capacitor C₂ is set to a value corresponding to the resistance value of the resistor R₂. Hence, the impedance value of the capacitor C₁ is higher than the impedance value of the capacitor C₂. In other words, an electrostatic capacitance value of the capacitor C₁ is lower than an electrostatic capacitance value of the capacitor C₂. Since the resistance value of the resistor R₁ is about five times the resistance value of the resistor R₂, it is exemplified that the impedance value of the capacitor C₁ is about five times the impedance value of the capacitor C₂. In other words, it is exemplified that the electrostatic capacitance value of the capacitor C₁ is about one fifth the electrostatic capacitance value of the capacitor C₂. For example, it is exemplified that the electrostatic capacitance value of the capacitor C₁ is about 12 pF (picofarads). It is exemplified that the electrostatic capacitance value of the capacitor C₂ is about 60 pF.

FIGS. 6 and 7 illustrate circuit simulation results of the equivalent circuit of the power amplifier circuit according to the comparative example. Specifically, FIG. 6 illustrates relationships between a frequency (megahertz (MHz)) of the power supply potential V_(CC) and amplitudes (decibel (dB)) of collector potentials of the first power amplifier 11 and the second power amplifier 12. FIG. 7 illustrates relationships between a frequency (MHz) of the power supply potential V_(CC) and phases (degree) of collector potentials of the first power amplifier 11 and the second power amplifier 12.

In FIG. 6 , a waveform 141 represents the amplitude of the collector potential of the first power amplifier 11. A waveform 142 represents the amplitude of the collector potential of the second power amplifier 12. The amplitude represented by the waveform 141 increases from about 100 MHz, whereas the amplitude represented by the waveform 142 decreases from about 100 MHz.

In FIG. 7 , a waveform 143 represents the phase of the collector potential of the first power amplifier 11. A waveform 144 represents the phase of the collector potential of the second power amplifier 12. The phase represented by the waveform 143 is delayed by about 4 degrees per about 100 MHz, whereas the phase represented by the waveform 144 is delayed by about 20 degrees per about 100 MHz. In other words, the phase of the collector potential of the first power amplifier 11 is ahead of the phase of the collector potential of the second power amplifier 12.

Thus, in a range of about 100 MHz or more in which a frequency of the power supply potential V_(CC) is asked to be in the 5G, a phase difference between the phase of the collector potential of the first power amplifier 11 and the phase of the collector potential of the second power amplifier 12 increases.

The phase of the collector potential of the first power amplifier 11 and the phase of the collector potential of the second power amplifier 12 do not coincide with each other, thereby resulting in the occurrence of distortion in the high-frequency output signal RF_(OUT).

For example, the case is discussed where the power supply circuit 103 controls the phase of the power supply potential V_(CC) so that the phase of the high-frequency input signal RF_(IN) and the phase of a collector potential of the transistor 111 in the first power amplifier 11 coincide with each other. In this case, the phases of a base potential and the collector potential of the transistor 111 in the first power amplifier 11 coincide with each other, and thus no distortion occur in the high-frequency signal RF_(M). However, the phase of the high-frequency signal RF_(M) and the phase of a collector potential of the transistor in the second power amplifier 12 do not coincide with each other. In other words, the phases of a base potential and the collector potential of the transistor in the second power amplifier 12 do not coincide with each other, and thus distortion occurs in the high-frequency output signal RF_(OUT).

Furthermore, for example, the case is discussed where the power supply circuit 103 controls the phase of the power supply potential V_(CC) so that the phase of the high-frequency signal RF_(M) and the phase of the collector potential of the transistor in the second power amplifier 12 coincide with each other. In this case, the phase of the high-frequency input signal RF_(IN) and the phase of the collector potential of the transistor 111 in the first power amplifier 11 do not coincide with each other. In other words, the phases of the base potential and the collector potential of the transistor 111 in the first power amplifier 11 do not coincide with each other, and thus distortion occurs not only in the high-frequency signal RF_(M) but also in the high-frequency output signal RF_(OUT).

First Embodiment

FIG. 8 illustrates a circuit configuration of a power amplifier circuit according to the first embodiment.

Of components in a power amplifier circuit 1, components that are the same as those in the power amplifier circuit 104 according to the comparative example are denoted by the same reference numerals, and a description thereof is omitted. Although the power amplifier circuit 1 may be implemented by a hybrid integrated circuit (which may be referred to as a module) in which a plurality of components (semiconductor integrated circuits and so forth) are mounted on one substrate, the present disclosure is not limited to this.

Although the power amplifier circuit 1 includes two stages of power amplifiers that are the first power amplifier 11 and the second power amplifier 12, the present disclosure is not limited to this. The power amplifier circuit 1 may include three or more stages of power amplifiers. For example, the power amplifier circuit 1 may further include one or more power amplifiers inserted between the first power amplifier 11 and the second power amplifier 12.

The power supply circuit 103 is electrically connected to the first power supply terminal 23 and the second power supply terminal 24 using an external power supply line 31. One end of the external power supply line 31 is electrically connected to the power supply circuit 103. The external power supply line 31 is divided into a first external power supply line 31 b and a second external power supply line 31 c at a branch portion 31 a. A tip portion of the first external power supply line 31 b is electrically connected to the first power supply terminal 23. A tip portion of the second external power supply line 31 c is electrically connected to the second power supply terminal 24.

In this embodiment, although the first external power supply line 31 b and the second external power supply line 31 c are integrally formed, the present disclosure is not limited to this. The first external power supply line 31 b and the second external power supply line 31 c may be separately formed and connected together. Furthermore, the first external power supply line 31 b and the second external power supply line 31 c do not have to be connected together. In other words, each of the other end portion of the first external power supply line 31 b and the other end portion of the second external power supply line 31 c may be directly connected to the power supply circuit 103.

FIG. 9 illustrates the power amplifier circuit according to the first embodiment. Specifically, FIG. 9 illustrates the power amplifier circuit 1 that is a semiconductor integrated circuit (IC) mounted on the substrate 131 as viewed from above.

On the substrate 131, the external power supply line 31 is formed. The external power supply line 31 is divided into the first external power supply line 31 b and the second external power supply line 31 c at the branch portion 31 a.

On a lower surface of the power amplifier circuit 1 (a surface opposite to the substrate 131), the first power supply terminal 23 and the second power supply terminal 24 are provided. The first power supply terminal 23 is electrically connected to the first external power supply line 31 b. The second power supply terminal 24 is electrically connected to the second external power supply line 31 c.

The width of the first external power supply line 31 b is narrower than the width of the second external power supply line 31 c. Furthermore, the length of the first external power supply line 31 b is longer than the length of the second external power supply line 31 c. Hence, an inductance value of the first external power supply line 31 b is higher than an inductance value of the second external power supply line 31 c.

In general, in power amplifiers connected in multiple stages, the size of a subsequent-stage power amplifier is larger than that of a previous-stage power amplifier. In other words, a collector current of the subsequent-stage second power amplifier 12 is higher than that of the previous-stage first power amplifier 11. Hence, it is desirable to reduce the inductance value of the second external power supply line 31 c as much as possible to reduce power loss in the second power amplifier 12. In other words, it is desirable to increase the width of the second external power supply line 31 c as much as possible and to reduce the length of the second external power supply line 31 c as much as possible.

An equivalent circuit of the power amplifier circuit 1 is the same as the equivalent circuit of the power amplifier circuit 104 (see FIG. 5 ). Note that an inductance value of the inductor L₁ differs from that in the power amplifier circuit 104.

An inductance value of the inductor L₁ is set to a value higher than an inductance value of the inductor L₂. Although it is exemplified that the inductance value of the inductor L₁ is set in accordance with a ratio of a resistance value of the resistor R₁ to a resistance value of the resistor R₂, and the inductance value of the inductor L₂, the present disclosure is not limited to this. For example, it is exemplified that the inductance value of the inductor L₁ is set to the product of a ratio of the resistance value of the resistor R₁ to the resistance value of the resistor R₂ and the inductance value of the inductor L₂. Here, the ratio of the resistance value of the resistor R₁ to the resistance value of the resistor R₂ is about five times. Hence, it is exemplified that the inductance value of the inductor L₁ is set to about five times the inductance value of the inductor L₂. For example, it is exemplified that, if the inductance value of the inductor L₂ is about 2 nH, the inductance value of the inductor L₁ is set to about 10 nH.

FIGS. 10 and 11 illustrate circuit simulation results of the equivalent circuit of the power amplifier circuit according to the first embodiment. Specifically, FIG. 10 illustrates relationships between a frequency (MHz) of the power supply potential V_(CC) and amplitudes (dB) of collector potentials of the first power amplifier 11 and the second power amplifier 12. FIG. 11 illustrates relationships between a frequency (MHz) of the power supply potential V_(CC) and phases (degree) of collector potentials of the first power amplifier 11 and the second power amplifier 12.

In FIG. 10 , a waveform 151 represents the amplitude of the collector potential of the first power amplifier 11. A waveform 152 represents the amplitude of the collector potential of the second power amplifier 12. The waveform 142, the waveform 151, and the waveform 152 substantially coincide with one another.

In FIG. 11 , a waveform 153 represents the phase of the collector potential of the first power amplifier 11. A waveform 154 represents the phase of the collector potential of the second power amplifier 12. The waveform 144, the waveform 153, and the waveform 154 substantially coincide with one another. In other words, a phase difference between the phase of the collector potential of the first power amplifier 11 and the phase of the collector potential of the second power amplifier 12 is controlled to be substantially zero.

SUMMARY

The power amplifier circuit 1 can reduce a phase difference between the phase of a collector potential of the transistor 111 in the first power amplifier 11 and the phase of a collector potential of the transistor in the second power amplifier 12. Thus, the power amplifier circuit 1 can reduce the possibility that distortion may occur in the high-frequency output signal RF_(OUT).

For example, the case is discussed where the power supply circuit 103 controls the phase of the power supply potential V_(CC) so that the phase of the high-frequency input signal RF_(IN) and the phase of the collector potential of the transistor 111 in the first power amplifier 11 coincide with each other. In this case, the phases of a base potential and the collector potential of the transistor 111 in the first power amplifier 11 coincide with each other, and thus the possibility is reduced that distortion may occur in the high-frequency signal RF_(M). Furthermore, the phase of the high-frequency signal RF_(M) and the phase of the collector potential of the transistor in the second power amplifier 12 coincide with each other. In other words, the phases of a base potential and the collector potential of the transistor in the second power amplifier 12 coincide with each other, and thus the possibility is reduced that distortion may occur in the high-frequency output signal RF_(OUT).

Second Embodiment

FIG. 12 illustrates a circuit configuration of a power amplifier circuit according to a second embodiment.

Of components in a power amplifier circuit 2, components that are the same as those in the power amplifier circuit 1 according to the first embodiment or the power amplifier circuit 104 according to the comparative example are denoted by the same reference numerals, and a description thereof is omitted. Although the power amplifier circuit 2 may be implemented by a hybrid integrated circuit (which may be referred to as a module) in which a plurality of components (semiconductor integrated circuits and so forth) are mounted on one substrate, the present disclosure is not limited to this.

The power supply circuit 103 is electrically connected to a power supply terminal 25 using an external power supply line 32.

One end of a first internal power supply line 17 is electrically connected to the power supply terminal 25. The other end of the first internal power supply line 17 is electrically connected to the first power amplifier 11 (the other end of the inductor 113 (see FIG. 3 )). One end of a second internal power supply line 18 is electrically connected to the power supply terminal 25. The other end of the second internal power supply line 18 is electrically connected to the second power amplifier 12.

An equivalent circuit of the power amplifier circuit 2 is the same as the equivalent circuit of the power amplifier circuit 104 (see FIG. 5 ).

In general, in power amplifiers connected in multiple stages, the size of a subsequent-stage power amplifier is larger than that of a previous-stage power amplifier. In other words, a collector current of the final-stage second power amplifier 12 is higher than that of the first-stage first power amplifier 11. Hence, it is desirable to reduce an inductance value of the second internal power supply line 18 as much as possible to reduce power loss in the second power amplifier 12. In other words, it is desirable to increase the width of the second internal power supply line 18 as much as possible and to reduce the length of the second internal power supply line 18 as much as possible.

An inductance value of the first internal power supply line 17 is set to a value higher than the inductance value of the second internal power supply line 18. Although it is exemplified that the inductance value of the first internal power supply line 17 is set in accordance with a ratio of a resistance value of the resistor R₁ to a resistance value of the resistor R₂, and the inductance value of the second internal power supply line 18, the present disclosure is not limited to this. For example, it is exemplified that the inductance value of the first internal power supply line 17 is set to the product of a ratio of the resistance value of the resistor R₁ to the resistance value of the resistor R₂ and the inductance value of the second internal power supply line 18. Here, the ratio of the resistance value of the resistor R₁ to the resistance value of the resistor R₂ is about five times. Hence, it is exemplified that the inductance value of the first internal power supply line 17 is set to about five times the inductance value of the second internal power supply line 18. For example, it is exemplified that, if the inductance value of the second internal power supply line 18 is about 2 nH, the inductance value of the first internal power supply line 17 is set to about 10 nH.

Various mounting methods for setting the inductance value of the first internal power supply line 17 to a value higher than the inductance value of the second internal power supply line 18 are conceivable. For example, it is considered that the width of the first internal power supply line 17 is made narrower than that of the second internal power supply line 18. Furthermore, it is considered that the length of the first internal power supply line 17 is made longer than that of the second internal power supply line 18.

FIG. 13 illustrates an example of the first internal power supply line of the power amplifier circuit according to the second embodiment. As illustrated in FIG. 13 , the first internal power supply line 17 may be wound in a helical fashion. This can make the length of the first internal power supply line 17 longer even in a situation in which a region is restricted, and thus the inductance value of the first internal power supply line 17 can be increased.

Furthermore, an inductor (component) may be inserted in the first internal power supply line 17.

FIG. 14 illustrates an inductor inserted in the first internal power supply line of the power amplifier circuit according to the second embodiment. An inductor 41, which is a surface mount device (SMD) illustrated in FIG. 14 , may be inserted in the first internal power supply line 17. Thus, the inductance value of the first internal power supply line 17 can be increased.

The power amplifier circuit 2 according to the second embodiment achieves the same effect as the power amplifier circuit 1 according to the first embodiment.

Third Embodiment

FIG. 15 illustrates a circuit configuration of a power amplifier circuit according to a third embodiment.

Of components in a power amplifier circuit 3, components that are the same as those in the power amplifier circuit 1 according to the first embodiment, the power amplifier circuit 2 according to the second embodiment, or the power amplifier circuit 104 according to the comparative example are denoted by the same reference numerals, and a description thereof is omitted. Although the power amplifier circuit 3 may be implemented by a hybrid integrated circuit (which may be referred to as a module) in which a plurality of components (semiconductor integrated circuits and so forth) are mounted on one substrate, the present disclosure is not limited to this.

The power supply circuit 103 is electrically connected to the first power supply terminal 23 and the second power supply terminal 24 using the external power supply line 121. One end of the external power supply line 121 is electrically connected to the power supply circuit 103. On another end side of the external power supply line 121, a division has been made into the first external power supply line 121 b and the second external power supply line 121 c at the branch portion 121 a. A tip portion of the first external power supply line 121 b is electrically connected to the first power supply terminal 23. A tip portion of the second external power supply line 121 c is electrically connected to the second power supply terminal 24.

One end of a second internal power supply line 52 is electrically connected to the second power supply terminal 24. The other end of the second internal power supply line 52 is electrically connected to the second power amplifier 12. One end of the capacitor 16 is electrically connected to the second power amplifier 12.

In general, in power amplifiers connected in multiple stages, the size of a subsequent-stage power amplifier is larger than that of a previous-stage power amplifier. In other words, a collector current of the subsequent-stage second power amplifier 12 is higher than that of the previous-stage first power amplifier 11. Hence, it is desirable to reduce an inductance value of the second internal power supply line 52 as much as possible to reduce power loss in the second power amplifier 12. In other words, it is desirable to increase the width of the second internal power supply line 52 as much as possible and to reduce the length of the second internal power supply line 52 as much as possible.

One end of a first internal power supply line 51 is electrically connected to the other end of the second internal power supply line 52. The other end of the first internal power supply line 51 is electrically connected to the first power amplifier 11 (the other end of the inductor 113 (see FIG. 3 )). One end of the capacitor 15 is electrically connected to the first power amplifier 11 (the other end of the inductor 113).

It is exemplified that an inductance value of the first internal power supply line 51 is set to a value that causes a delay corresponding to a phase difference between the waveform 143 and the waveform 144 illustrated in FIG. 7 . Thus, the power amplifier circuit 3 enables the phase of a collector potential of the first power amplifier 11 and the phase of a collector potential of the second power amplifier 12 to coincide with each other.

Incidentally, the inductance value of the first internal power supply line 51 exceeds a design value (set value) and becomes too high in actuality, and there is a possibility that the phase of a collector potential of the transistor 111 in the first power amplifier 11 may actually lag behind the phase of a collector potential of the transistor in the second power amplifier 12. Thus, the power amplifier circuit 3 desirably further includes a capacitor 53 between the first power amplifier 11 (the other end of the inductor 113 (see FIG. 3 )) and the first power supply terminal 23. The capacitor 53 functions as a feed-forward capacitor and plays a role in compensating for a delay in the phase (in advancing the phase) of the collector potential of the transistor 111 in the first power amplifier 11.

FIG. 16 illustrates an equivalent circuit of the power amplifier circuit according to the third embodiment. An equivalent circuit of the power amplifier circuit 3 includes the inductors L₁ and L₂, the resistors R₁ and R₂, and capacitors C₁, C₂ and C₃.

The inductor L₂ corresponds to an inductance component of the second internal power supply line 52. The inductor L₁ corresponds to an inductance component of the first internal power supply line 51. The capacitor C₃ corresponds to the capacitor 53.

The power supply potential V_(CC) is not only transmitted to the resistor R₁ (corresponding to the first power amplifier 11) through the inductor L₂ and L₁ but also transmitted (fed forward) to the resistor R₁ through the capacitor C₃.

In the power amplifier circuit 3, the one end of the first internal power supply line 51 is electrically connected to the other end of the second internal power supply line 52, thereby making it possible to reduce a phase difference between the phase of the collector potential of the transistor 111 in the first power amplifier 11 and the phase of the collector potential of the transistor in the second power amplifier 12. Hence, the power amplifier circuit 3 can reduce the possibility that distortion may occur in the high-frequency output signal RF_(OUT).

The power amplifier circuit 3 further includes the capacitor C₃ and thereby can adjust the phase of the collector potential of the transistor 111 in the first power amplifier 11. Thus, the power amplifier circuit 3 can reduce further a phase difference between the phase of the collector potential of the transistor 111 in the first power amplifier 11 and the phase of the collector potential of the transistor in the second power amplifier 12. Hence, the power amplifier circuit 3 can reduce further the possibility that distortion may occur in the high-frequency output signal RF_(OUT).

The above-described embodiments are intended to facilitate understanding of the present disclosure but are not intended for a limited interpretation of the present disclosure. The present disclosure can be changed or improved without departing from the gist thereof and encompasses equivalents thereof.

While embodiments of the disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The scope of the disclosure, therefore, is to be determined solely by the following claims. 

What is claimed is:
 1. A power amplifier circuit comprising: a plurality of power amplifiers connected in multiple stages, and configured to amplify a high-frequency input signal and to output an amplified high-frequency output signal; a first power supply terminal electrically connected to a first power amplifier of the plurality of power amplifiers; a second power supply terminal electrically connected to a second power amplifier of the plurality of power amplifiers, the second power amplifier being subsequent to the first power amplifier; a first external power supply line configured to electrically connect a power supply circuit to the first power supply terminal, the power supply circuit being configured to output a power supply potential corresponding to an amplitude level of the high-frequency input signal; and a second external power supply line configured to electrically connect the power supply circuit to the second power supply terminal, wherein an inductance value of the first external power supply line is greater than an inductance value of the second external power supply line, or wherein a width of the first external power supply line is narrower than a width of the second external power supply line.
 2. The power amplifier circuit according to claim 1, wherein the inductance value of the first external power supply line is greater than the inductance value of the second external power supply line.
 3. The power amplifier circuit according to claim 1, wherein the width of the first external power supply line is narrower than the width of the second external power supply line.
 4. The power amplifier circuit according to claim 1, wherein: the inductance value of the first external power supply line is greater than the inductance value of the second external power supply line, and the width of the first external power supply line is narrower than the width of the second external power supply line.
 5. The power amplifier circuit according to claim 1, wherein a length of the first external power supply line is longer than a length of the second external power supply line.
 6. The power amplifier circuit according to claim 2, wherein a length of the first external power supply line is longer than a length of the second external power supply line.
 7. The power amplifier circuit according to claim 1, wherein: the inductance value of the first external power supply line is greater than the inductance value of the second external power supply line, and a length of the first external power supply line is longer than a length of the second external power supply line.
 8. A power amplifier circuit comprising: a plurality of power amplifiers connected in multiple stages, and configured to amplify a high-frequency input signal and to output an amplified high-frequency output signal; a power supply terminal configured to receive a power supply potential, the power supply potential corresponding to an amplitude level of the high-frequency input signal; a first internal power supply line configured to electrically connect a first power amplifier of the plurality of power amplifiers to the power supply terminal; and a second internal power supply line configured to electrically connect a second power amplifier of the plurality of power amplifiers to the power supply terminal, the second power amplifier being subsequent to the first power amplifier, wherein an inductance value of the first internal power supply line is greater than an inductance value of the second internal power supply line, or wherein a width of the first internal power supply line is narrower than a width of the second internal power supply line.
 9. The power amplifier circuit according to claim 8, wherein the inductance value of the first internal power supply line is greater than the inductance value of the second internal power supply line.
 10. The power amplifier circuit according to claim 8, wherein the width of the first internal power supply line is narrower than the width of the second internal power supply line.
 11. The power amplifier circuit according to claim 8, wherein: the inductance value of the first internal power supply line is greater than the inductance value of the second internal power supply line, and the width of the first internal power supply line is narrower than the width of the second internal power supply line.
 12. The power amplifier circuit according to claim 8, wherein a length of the first internal power supply line is longer than a length of the second internal power supply line.
 13. The power amplifier circuit according to claim 8, wherein: the inductance value of the first internal power supply line is greater than the inductance value of the second internal power supply line, and a length of the first internal power supply line is longer than a length of the second internal power supply line.
 14. The power amplifier circuit according to claim 8, further comprising: an inductor in the first internal power supply line.
 15. The power amplifier circuit according to claim 8, wherein: the inductance value of the first internal power supply line is greater than the inductance value of the second internal power supply line, and an inductor in the first internal power supply line.
 16. A power amplifier circuit comprising: a plurality of power amplifiers connected in multiple stages, and configured to amplify a high-frequency input signal and to output an amplified high-frequency output signal; a second power supply terminal configured to receive a power supply potential, the power supply potential corresponding to an amplitude level of the high-frequency input signal; a second internal power supply line having a first end electrically connected to the second power supply terminal, and a second end electrically connected to a second power amplifier of the plurality of power amplifiers; a first internal power supply line having a first end electrically connected to the second end of the second internal power supply line, and a second end electrically connected to a first power amplifier of the plurality of power amplifiers, the second power amplifier being subsequent to the first power amplifier; a first power supply terminal configured to receive the power supply potential; and a capacitor electrically connected between the first power supply terminal and the second end of the first internal power supply line. 